THE SEQUENCE STRATIGRAPHY OF NIGER DELTA, DELTA FIELD, OFFSHORE NIGERIA A Thesis by AJIBOLA OLAOLUWA DAVID OWOYEMI Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2004 Major Subject: Geology SEQUENCE STRATIGRAPHY OF NIGER DELTA, DELTA FIELD, OFFSHORE NIGERIA A Thesis by AJIBOLA OLAOLUWA DAVID OWOYEMI Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved as to style and content by: _______________________ _______________________ Brian J. Willis Steven L. Dorobek (Chair of Committee) (Member) _________________________ _________________________ Jerry L. Jensen Richard F. Carlson (Member) (Head of Department) August 2004 Major Subject: Geology iii ABSTRACT Sequence Stratigraphy of the Niger Delta, Delta Field, Offshore Nigeria. (August 2004) Ajibola Olaoluwa David Owoyemi, B. Tech (Honors), Federal University of Technology, Akure, Nigeria; M.B.A., Federal University of Technology, Akure, Nigeria Chair of Advisory Committee: Dr. Brian J. Willis The Niger Delta clastic wedge formed along the West Africa passive margin. This wedge has been divided into three formations that reflect long-term progradation: 1) pro-delta shales of the Akata Formation (Paleocene to Recent), 2) deltaic and paralic facies of the Agbada Formation (Eocene to Recent) and 3) fluviatile facies of the Benin Formation (Oligocene-Recent). This study combines a three-dimensional seismic image with well log data from Delta field to describe lithic variations of the Agbada Formation and develop a sequence stratigraphic framework. The 5000-feet thick Agbada Formation in Delta field is divided by five major sequence boundaries, each observed in seismic cross sections to significantly truncate underlying strata. Sequence boundaries developed as mass flows eroded slopes steepened by the structural collapse of the Niger Delta clastic wedge. Basal deposits directly overlying areas of deepest incision along sequence boundaries formed by the migration of large, sinuous turbidite channels. Upward- coarsening sets of inclined beds, hundreds of feet thick, record progradation of deltas iv into turbidite-carved canyons and onto down faulted blocks. Thinner, more continuous seismic reflections higher within sequences are associated with blocky and upward- fining well-log patterns interpreted to reflect deposition in shoreline, paralic, and fluvial environments. Episodes of structural collapse of the Niger Delta clastic wedge appear to be associated with progradation of Agbada Formation sediments and the loading of underlying Akata Formation shales. Progradation may have been more rapid during third order eustatic sea level falls. Effects of syn-sedimentary deformation on patterns of sediment transport and deposition are more pronounced in lower sequences within the Agbada Formation, and include: 1) incision into foot walls of listric normal faults, 2) abrupt reorientation of channelized flow pathways across faults, and 3) thinning of deposits across crests of rollover anticlines on down thrown fault blocks. Structural controls on deposition are less pronounced within younger sequences and canyon incisions along sequence boundaries are more pronounced, suggesting that the locus of sediment accumulation and structural collapse of the clastic wedge moved farther basinward as accommodation was filled in the area of Delta field. v DEDICATION This work is dedicated to the glory of God and to the memory of my late father, Mr. William Owoyemi, my mother, Mrs. Fatimat Owoyemi, my wife, Mrs. Monisola Owoyemi and my kids, Olubanke and Olaoluwa Owoyemi. vi ACKNOWLEDGEMENTS I would like to express my special thanks to Dr. Brian Willis, the Chair of my thesis committee, for his assistance and invaluable contribution to the success of this work. My sincere gratitude to Dr. Steve Dorobek for reading the manuscript. I also appreciate Dr. Jerry Jensen’s assistance and contribution in reviewing the manuscript. I am my indebted to my company, ChevronTexaco Nigeria Limited, for providing a scholarship and data for the study. I am also grateful to my supervisor in the office Dr. Stan Franklin and Mr. Rotimi Adenuga for their unflinching support and encouragement. I am sincerely grateful to the numerous persons who have made invaluable contributions toward the successful completion of my master degree program, Shirley Smith of ChevronTexaco overseas, Mr Wale Ogundana and Basir Koledoye ChevronTexaco Nigeria Limited. I also appreciate my wife and kids for being with me during the program period. vii TABLE OF CONTENTS Page ABSTRACT………………………………………………………..…................ iii DEDICATION……………………………………………………………... ....... v ACKNOWLEDGEMENTS………………………………………….……… .... vi TABLE OF CONTENTS…………………………….……………..…............... vii LIST OF FIGURES……………………………………………….…………...... ix LIST OF TABLES………………………………………………..….………...... xi INTRODUCTION……………………………………………………………..... 1 THE NIGER DELTA………………………………………………………….... 5 Regional Setting………………………………………………............... 5 Niger Delta Stratigraphy……………………………………………...... 10 Niger Delta Petroleum System………………………………................ 15 LOCATION AND METHODOLOGY………………………………………..... 18 Location……………………………………………………………....... 18 Database……………………………………………………………....... 19 Methodology………………………………………………………........ 19 STRATIGRAPHY OF DELTA FIELD……………………………………….... 25 Seismic Cross Sections of Delta Field………………………………...... 29 Offset of Stratigraphic Surfaces across Faults………………................. 35 Sequence within Delta Field…………………………………................. 56 DISCUSSION ………………………………………………………………....... 73 Implication on Hydrocarbon Exploration…………………………........ 79 viii Page CONCLUSIONS……………………………………………………………...... 81 REFERENCES CITED……………………………………………………….... 83 VITA…………………………………………………..……………………...... 88 ix LIST OF FIGURES FIGURE Page 1 Location map of study area. …………………………………………......... 3 2 Niger Delta lithostratigraphy….………………………………………....... 6 3 Niger Delta oil field structures and associated traps…………………........ 9 4 Stratigraphic column showing formations of the Niger Delta………......... 11 5 Reflection patterns and sequence boundary geometry observed in seismic cross sections near Delta field………………………………..... 20 6 Correlation chart of gamma ray logs in Delta field……………………..... 21 7 Types of well log patterns observed in Delta field……………………...... 26 8 Biostratigraphic zonation within Delta-2 Well………………………........ 28 9 Seismic cross section along line aa’…………………………………........ 30 10 Seismic cross section along line cc’………………………………… ........ 31 11 Seismic cross section along line bb’…………………………………....... 32 12 Seismic cross section along line dd’…………………………………....... 33 13 Structure map of sequence boundary 1………………………………....... 36 14 Structure map of sequence boundary 2………………………………........ 37 15 Structure map of sequence boundary 3………………………………........ 38 16 Structure map of sequence boundary 4………………………………........ 39 17 Structure map of sequence boundary 5………………………………........ 40 18 Structure map of intra-sequence 1…………………………………........... 41 x FIGURE Page 19 Structure map of intra-sequence 2………………………………...……... 42 20 Structure map of intra-sequence 3…………………………….. ….......... 43 21 Structure map of intra-sequence 4………………………………..……... 44 22 Structure map of intra-sequence 5………………………………………. 45 23 Isolith map between sequence boundary 1 and intra-sequence surface 1.. 47 24 Isolith map between sequence boundary 2 and intra-sequence surface 2.. 48 25 Isolith map between sequence boundary 3 and intra-sequence surface 3.. 49 26 Isolith map between sequence boundary 4 and intra-sequence surface 4.. 50 27 Isolith map between sequence boundary 5 and intra-sequence surface 5.. 51 28 Isolith map between intra-sequence surfaces 1 and 2……………..…….. 52 29 Isolith map between intra-sequence surfaces 2 and 3…………………… 53 30 Isolith map between intra-sequence surfaces 3 and 4…………………… 54 31 Isolith map between intra-sequence surfaces 4 and 5…………………… 55 32 Seismic horizon slices on sequence boundary 1……………………..….. 59 33 Seismic horizon slice on sequence boundary 2………………………...... 64 34 Seismic horizon slice on sequence boundary 3………………………….. 66 35 Seismic horizon slice on sequence boundary 4………………………...... 68 36 Seismic horizon slice on sequence boundary 5…………………….…..... 71 37 Aggrading channel drafted from time horizon slices on SB 5…............... 72 38 Sequence boundary development on down faulted blocks……….…….. 78 xi LIST OF TABLES TABLE Page 1 Table of formations Niger Delta area, Nigeria…… ………….….......... 12 2 Hydrocarbon habitat table…………………………..……………......... 16 1 INTRODUCTION The 12 km thick Niger Delta clastic wedge spans a 75, 000 km2 area in southern Nigeria and the Gulf of Guinea offshore Nigeria. This clastic wedge contains the 12th largest known accumulation of recoverable hydrocarbons, with reserves exceeding 34 billion barrels of oil and 93 trillion cubic feet of gas (Tuttle et al., 1999). These deposits have been divided into three large-scale lithostratigraphic units: (1) the basal Paleocene to Recent pro-delta facies of the Akata Formation, (2) Eocene to Recent, paralic facies of the Agbada Formation, and (3) Oligocene-Recent, fluvial facies of the Benin Formation (Evamy et al., 1978; Short and Stauble, 1967; Whiteman, 1982). These formations become progressively younger farther into the basin, recording the long-term progradation of depositional environments of the Niger Delta onto the Atlantic Ocean passive margin.